Global warming may be contributing to a "catastrophic" decline in stocks of wild Atlantic salmon, according to the director of the Salmon Research Agency, Dr Ken Whelan. Speaking at the Fifth International Atlantic Salmon Symposium in Galway, he said the overall salmon catch in Ireland had declined from an average of 600,000 fish in 1980 to 120,000 this year.
"In recent years, we have seen the catch decline to a level of 350,000 to 400,000, but this year's levels can only be described as catastrophic," said Dr Whelan.
Some 1,400 families are involved in the £2 million commercial salmon fishery. The growing angling sector is now worth an estimated £13 million per year in tourism and other revenues.
Dr Whelan said it was unfair to blame drift-net fishermen for the decline. Although over-fishing and problems with river habitats had contributed to it in the past, a new and worrying phenomenon had emerged in the 1990s.
This was the marked decrease in the survival rate of salmon during the oceanic phase of their life-cycle. Research had "conclusively linked" this decrease to temperature changes in critical feeding grounds in the north-west Atlantic.
In the ocean, salmon feed at between 4C and 7C, according to Dr Whelan. Their increased mortality in recent years could indicate that global climate change had now reached a critical point where it was beginning to have a major impact on ecosystems. If this was the case, then the future survival rates of salmon could be used as a sensitive "barometer" of climate change.
A research scientist at the Department of Fisheries and Oceans in Canada, Dr David Reddin, said the decline in stocks could be directly related to temperature changes in the north-west Atlantic.
As commercial drift-netting for salmon had been largely curtailed during the 1990s, it was "reasonable" to assume that climatic change was responsible. However, more research was needed to establish the link between temperature changes and lower salmon survival rates.
"Recent downturns in salmon abundance in the late 1980s and 1990s are unprecedented in magnitude and, once again, have drawn attention to our lack of knowledge of salmon life history," Dr Reddin said.
Overall stocks of the larger north Atlantic salmon were thought to be the lowest on record. "Other north Atlantic salmon stocks are also in decline. For example, downturns in rod catches of Scottish spring salmon (springers), which began in the late 1970s, have continued into the 1990s, with a marked increase in the rate of decline."
The widespread decline had led scientists to conclude that it was related to the ocean life of the salmon. "For many of the rivers where sea survival is measured, the lowest recorded values have occurred in recent years.
"These low survivals have coincided with greatly reduced marine exploitation achieved through massive reductions in effort, or in some cases, complete bans, leaving us with the conclusion that something other than exploitation is the main cause."
More than 200 scientists from 10 countries are attending the conference, which takes place every seven years.